1. Field of the Invention
The present invention relates, generally, to medical devices and methods. More particularly, the invention relates to a method of making medical devices. Most particularly, it relates to a device and method for making a balloon catheter device. The balloon catheter may be used for angioplasty, stent delivery, or other interventional or diagnostic procedures.
2. Background Information
Referring to FIGS. 1 and 2, a catheter balloon 200 is relatively long and generally cylindrical when inflated. The balloon may be provided in various size, diameters and lengths. Balloon catheters are used to treat disease by being inflated in a blood vessel to improve the path for blood flow and/or to deploy a stent. The balloon is at or near the end of a long catheter shaft, which typically comprises an inner element 201 and an outer element 202, which is inserted into an appropriate blood vessel, then threaded through the circulatory system to reach the treatment site. The balloon is inflated by pressurizing it via the hollow catheter, using a pressure source outside the body. Balloons are made of a very thin but rather rigid plastic, so that the inflated diameter is predictable and doesn't vary greatly as a function of inflation pressure. Because of this, catheter balloons do not stretch like a rubber balloon when inflated, but rather they unfold.
Referring to FIG. 3, prior to inflation and during threading through the vascular system, the balloon must be folded in an orderly manner to make it as compact as possible to facilitate catheter advancement through the vascular system. The folded balloon has several approximately equal-sized lobes or “wings”, which wrap in the same direction around the catheter shaft.
Balloons are folded in two steps, which are referred to herein as “pleating” and “folding”.
Referring to FIG. 4, pleating is the process of dividing the circumference of the balloon into equal-sized wings or pleats 205, which, after pleating, extend radially outward from the center.
Folding is the process of wrapping the wings spirally around the catheter shaft. Folding is typically done by hand, holding the shaft in one hand while gripping and turning the adjacent part of the balloon around the catheter axis with the other hand. The balloon is folded incrementally, moving both the folding and grasping hands incrementally in steps from the proximal to the distal end of the balloon. Following the folding, the plastic balloon is typically placed in a tube or sheath to hold it in the folded position then placed at an elevated temperature for some time to set it so that it will tend to remain in the folded, lowest profile position.
Existing technology is believed to have significant limitations and shortcomings. A hand-folding process in use tends to cause a slight helix in the balloon because a torque is required to fold the wings spirally around the shaft. This torque exists between the folding hand and the grasping hand of the person folding the balloon and is evidenced by the fact that it is necessary to grasp the catheter in order to fold the balloon. Another problem with the hand-folding process is that it tends to have variable and inconsistent results. Another problem is that the manual process adds a significant labor cost to the product.
A machine folding processes attempts to fold the entire balloon at once, rather than incrementally, while grasping the catheter shaft adjacent to the balloon. The machine and process tends to be unsuccessful in folding the balloon because there is a much greater torque required to fold the entire balloon at once, and the catheter shaft, which is small in diameter and made of plastic, is unable to support the required torsion and simply deflects torsionally, or twists.
The present invention provides a folding apparatus and method which are believed to constitute an improvement over existing technology.